As the power supply for a medical implant comprising electronic components (e.g., a cardiac pacemaker having wireless, and preferably bidirectional remote data transmission), galvanic elements such as, for example, batteries are required that have a large capacity and permit a high discharging current (e.g., in the mA range) to be drawn. High battery capacity extends the service life of the medical implant, thereby reducing the number of surgeries required to replace the battery and/or the implant. Additionally, a high discharging current (current pulse) must be drawn at least briefly for remote data transmission.
Implants used in human medicine for cardiac therapy are typically programmed during the implantation procedure. The programming is usually performed using a programming head which must be positioned directly over the implant. Since said programming head cannot be sterilized for use in the operating room, it must be embedded in a sterile casing. To avoid the effort required to bring a programming head into the operating room in a sterile manner, a new generation of medical implants for cardiac therapy will permit the implant to be programmed using radio signals. The battery of the implant must have a particularly high power density at the beginning of the discharge for said programming, which is carried out wirelessly. To attain said high power densities, the voltage of the battery used for the power supply should be as high as possible, and the internal resistance thereof should be as low as possible.
Galvanic elements such as, for example, batteries are electrochemical energy accumulators and energy converters. The basic components of a galvanic element are: a first electrode which comprises or is composed of a first active material; a second electrode which comprises or is composed of a second active material; and an electrolyte which connects the two electrodes. In the discharge process, the stored chemical energy is converted to electrical energy by an electrochemical redox reaction involving the oxidation of the first active material with release of electrons at a first electrode (e.g., anode, negative electrode in terms of the discharge process), and the reduction of the second active material with acquisition of electrons at a second electrode (e.g., cathode, positive electrode in terms of the discharge process), thereby enabling current to be drawn from the galvanic element.
The capacity (the quantity of electricity that can be drawn), voltage, internal resistance, and other parameters of galvanic elements are influenced to a considerable extent by the composition of the active materials used in the electrodes. “Active materials” refers exclusively to those components of the electrodes of the galvanic element that are oxidized (at the anode) or reduced (at the cathode) upon discharge of the galvanic element, and that deliver electrical current via said electrode reactions. The active material of the cathode can comprise one or more reducible substances, and/or the active material of the anode can comprise one or more oxidizable substances.
In addition to the active materials defined above, the electrodes of galvanic elements typically contain further components that do not participate in the current-sourcing electrode reactions, and therefore do not contribute to the capacity of the galvanic element, but that are required for the reliable operation of the galvanic element, such as, for example, electronically conductive additives for increasing electronic conductance within the electrode, and/or binding agents to increase the robustness of the electrode.
Foreign patent application documents DE 10 2006 021 158 A1, DE 10 2005 059 375 A1, and EP 2 017 910, and U.S. Pat. No. 4,260,668 make known a battery comprising a positive electrode which contains copper oxyphosphate as the active material. Additionally, U.S. Pat. No. 4,448,864 discloses a lithium-manganese dioxide battery, the positive electrode of which contains manganese dioxide and copper oxyphosphate. Such batteries are suited, inter alia, for use to supply power to medical implants. Due to the above-described trends in the development of medical implants for, in particular, cardiac therapy, it is necessary to increase the voltage of such galvanic elements, in particular in the initial stage of the discharge process, and to increase the loadability upon discharge using current pulses.
The present invention is directed toward overcoming one or more of the above-identified problems.